Electronic tuning device for visual tuning of stringed instruments

ABSTRACT

An electronic tuning device for tuning stringed instruments provides a selectable sinusoidal reference frequency which is converted to pulses of the same frequency. The fading picked-up signal from a string of the instrument is passed to a high-gain saturating amplifier and converted to a sustained square wave which lasts of the order of 5 to 10 seconds as the string signal becomes minimal. The frequency of the square wave is then compared with the pulse frequency by supplying the pulses and the square waves to a comparator gate whose output controls a glow discharge lamp attached to the device. When the string of the instrument is tuned to bring the frequency of the square wave close to that of the pulses, the frequency difference to be minimized is indicated by the observable blink frequency of the lamp. The instrument responds similarly to one octave above the tuned frequency. Provision is also made to deliver the selected reference frequency to the usual musical instrument amplifier to enable aural tuning by a group of musicians.

United States Patent [191 Westhaver Mar. 27, 1973 [54] ELECTRONIC TUNINGDEVICE FOR VISUAL TUNING OF STRINGED INSTRUMENTS [76 Inventor: LawrenceA. Westhaver, 13001 Old Stagecoach Road. Laurel. Md.

221 Filed: June11,1971 21 Appl.No.: 152,246

52 US. cl... ..s4/454, 324/79 R 51 Int. Cl. ..G10g 7/02 58 Field OfSearch ..84/454; 324/791:

[56] References Cited UNITED STATES PATENTS 3,509,454 4/1970 Gossel...s4/454ux 3,180,199 4/1965 Anderson"... ....s4/4s4 2,207,450 7/1940Bergan et al. ....84/454 3,144,802 8/1964 Faber et al. ....84/4543,631,756 1/1972 Mackworth-Young ..84/454 Primary Examiner-Richard B.Wilkinson Assistant Examiner-John F. Gonzales Attamey-James W. Westhaver[57] ABSTRACT An electronic tuning device for tuning stringedinstruments provides a selectable sinusoidal reference frequency whichis converted to pulses of the same frequency. The fading picked-upsignal from a string of the instrument is passed to a high-gainsaturating amplifier and converted to a sustained square wave whichlasts of the order of 5 to 10 seconds as the string signal becomesminimal. The frequency of the square wave is then compared with thepulse frequency by supplying the pulses and the square waves to a Y 4Claims, 6 Drawing Figures SELECTABLE STANDARD PULSE DRIVER a FREQUENCY32:37: moiialoR OSCILLATOR L GUITAR SATURATING COMPARISON S'GNALAMPLIFIER m GATE PATENTEUHAR2H975 3,722,353

sum 1 or 5 SELECTABLE PULSE DRIVER a STANDARD m S'GNAL AMPLIFIER m GATELI Ll U L! U U H H H Fl H FIG. 3

INVENTOR LAWRENCE A. WESTHAVER PATEHTEDHmHm 3,122,353

sum 2 OF 5 INVENTOR LAWRENCE A. WESTHAVER PATENTEnnARznma SHEET 3 [IF 5Q GE mm @N INVENTOR LAWRENCE A. WESTHAVER PATENTEUmznma SHEET '4 OF 5INVENTOR LAWRENCE A. WESTHAVER mm m mm mm vm mm PATENTFDmzmu SHEET 5 [IF5 INVENTOR LAWRENCE A. WESTHAVER ELECTRONIC TUNING DEVICE FORVISUALTUNING OF STRINGED INSTRUMENTS PURPOSES OF THE INVENTION The presentinvention was developed to meet the need for a compact unitary devicecapable of visually accurate tuning of stringed instruments.

The primary object of the invention is to provide a relatively smallportable electronic device capable of accurate tuning by visualobservation of a lamp which indicates the disparity between stringfrequency and a standard frequency.

Another objec'tis to provide such a device with a selection of standardfrequencies for the various strings of a guitar or other stringedinstrument.

A further object is to provide such a device witha selection of standardfrequencies for input to the'usual instrument amplifier-speaker toenable aural tuning of other instrument in a band while also providingvisual tuning for the operator of the device.

THE PRIOR ART In' prior systems of the electronic tuning, agreement ofthe instrument pickup frequency has been sensed either visually oraudially. Various visual sensing arrangements are described in U. 8.Pat. No. 3,144,802 and include use of an oscilloscope, a stroboscope, ora digital'read-out of the frequency of the instrument being tuned.

Audialsensing is illustrated in U. S. Pat. No.

3,501,992, this patent employing a resistor-capacitor type of generatorfor the reference frequency. It is also known to use digital circuitryto compare the instrument frequency with a reference signal. In U. S.Pat. No. 3,472,116, digital circuitry is used to compare the dividedfrequencies representing the twelve tones of an octave.

SUMMARY OF THE PRESENT INVENTION In the present invention, the deviceincludes an electronic system compactly built into a casing havingdimensions of about two by .eight by eight inches and having in visibleposition a glow lamp responsive to the frequency disparity. The deviceis readily portable and may be mounted on a music stand or in the usualguitar instrument amplifier, or may be placed atop a piano. Within thecasing is an electronic system comprising a power supply, a generator ofselective reference frequencies, a high-gain saturating amplifier forthe string frequency being tuned, a comparator gate receiving thereference and string frequencies and a connection from the comparatorgate to the glow lamp to visually indicate the frequency difference. Thestring frequency from the pickup of the instrument is converted to asquare wave while the reference frequency is converted to pulses and thetwo are combined in the gate in such manner that the lamp is energizedby the gate only when square wave input and pulse input aresimultaneously present and in phase.

Connections to the device include a plug-in input cable from theinstrument pickup, an input cord for A. C. power and a plug-in outputcable from the device to deliver the reference frequency to the usualinstrument amplifier. However, if the device is. built into the usualamplifier for the musical instrument, the cable and cord connections maybe replaced by permanent wiring and a switch used to deliver the stringsignal either to the device or to the instrument amplifier.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a system diagram indicating themajor circuits involved.

FIG. 2 shows the device in a commercial package with appropriate inputand output.

FIG. 3 indicates the waveforms present at several points in the circuitfor a fundamental and an octave higher input.

FIG. 4 is a wiring diagram showing one embodiment of the pulse formingcircuit, saturating amplifier, comparison gate and driver and indicatorlamp.

FIG. 5 is a wiring diagram showing one embodiment of the selectablestandard frequency oscillator.

FIG. 6 is a wiring diagram of a power supply suitable for powering theabove mentioned circuits.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 a selectable standardfrequency oscillator provides for guitar tuning purposes, one of sixsinusoidal signals to the input of a pulse forming circuit. Thesinusoidal signals must have a high degree of frequency stability and atleast short term amplitude stability. For tuning a conventional electricguitar to American Standard pitch, the six frequencies should be: 82.4H,(E 110.0H (A 146.8H, (D 196.0H (G 246.9I-I (B and 329.6H, (E

With a sinusoidal signal input, the pulse forming circuit will produce asample pulse for every cycle of the input signal. The time duration ofthe sample pulse will be a fixed percentage of the period (l/f) of theinput signal. The duration of the sample pulse, determined by thecircuit parameters, is made significantly less than 25 percent of theperiod as will hereinafter be explained.

The sample pulse thus generated is presented to one input of a two-inputcomparison gate.

The signal produced by a plucked instrument string will approximate adamped sinusoid. If on an electric guitar the string is plucked at thetwelfth fret, a strong fundamental with a minimum of harmonics with beproduced by the pick-up. In any case the string should be plucked at themid-point of its effective length.

Since the signal from the string decays rapidly, if a usable output fromthe saturating amplifier is to be maintained for a protracted length oftime, i.e., 5 to 10 seconds, the amplifier must possess high gain. Thefunction of the saturating amplifier and its circuitry is to produce alasting square wave output signal ofthe same frequency as the dampedsinusoid string signal at the input of the amplifier.

This square wave signal is presented to the second input of thetwo-input comparison gate.

The comparison gate inputs are constrained to have signal swings limitedby ground and plus 3.6 volts. The comparison gate is of the NOR" type,i.e., if either input is high (near +3.6 volts) the output of the gatewill be low" (near-ground) and if both inputs are low" the output willbe high.

The comparison gate output will switch between two voltage levels. Theoutput voltage level corresponding to the condition of the inputs inwhich both inputs are at the level of the sample pulse will cause thedriver to turn on the indicator lamp which is an instantly responsiveneon type. When either one or both of the cornparison gate inputs arenot at the voltage level of the sample pulse, the output of thecomparison gate will be at the other voltage level and the driver willextinguish the lamp.

If the guitar signal causes the saturating amplifier to produce a squarewave that has exactly the same frequency as the selectable standardfrequency oscillator, the sample pulses and the square wave will haveone of the following time relationships: the square wave voltage levelis the same as the sample pulse when the sample pulse occurs, the squarewave voltage level is not the same as the sample pulse when thesamplepulse occurs, or the square wave is switching during the sample pulseduration.

In the first relationship the output of the comparison gate will be atrain of pulses (the sample pulses propagating thru) each one of whichwill cause the driverto light the indicator lamp for its duration..Theindicator lamp flashes with each sample pulse. Even the lowest musicalfrequency is higher than the highest visually perceivable flicker rate.Thus the eye perceives the indicator lamp, which is actually flashing ata rate determined by the selectable standard frequency oscillator, to beconstantly on.

In the second relationship the square wave voltage level is not the sameas the sample pulse and the output of the'comparison gate will be asteady voltage level which will, thru the driver, keep the lampextinguished.

In the third time relationship the square wave switches during theoccurrence of the sample pulse. The comparison gate output will be atrain of narrow pulses since the gate will propagate thru only thatportion of the sample pulse that occurs when the voltage level of thesquare wave is the same as the voltage level of the sample pulse.

If the guitar signal thru the saturating amplifier produces a squarewave that is slightly lower or higher in frequency than the output ofthe selectable standard frequency oscillator, the neon indicator lampwill appear to blink on and off. As an example let there be a one fifthof a cycle per second difference between the guitar signal and theselectable standard frequency oscillator. This means that the timerelationship (or phase) of the square wave will shift with respect tothe sample pulse and will be shifting at the rate of one cycle everyfive seconds. While the square wave voltage level is the same as thesample pulses during the pulses occurrence there will be an apparentsteady on condition of the indicator lamp. As the phase drifts the lampwill appear to dim as the sample pulse occurs while the square waveswitches and finally the lamp will extinguish as the voltage level ofthe square wave is different than that of the sample pulse during theoccurrence of the sample pulse. As long as there is a frequencydifference this drift will continue and there will be a blinking of theindicator lamp.

The blink rate as perceived by the eye may be used to determine thefrequency difference by the following formula:

Blinks/sec cycles/sec of frequency difference.

. string frequency and the standard frequency.

As previously noted the sample pulse width is made significantly lessthan 25 percent of the period of the fundamental. This is done in orderto achieve the same tuning indication when the guitar input is oneoctave higher in frequency. On a standard guitar depressing any stringon the twelfth fret will raise the pitch of the string by an octave ifthe bridge is properly adjusted. If after using the system to tune anopen string the string is depressed at the twelfth fret and plucked, thelamp flicker will indicate the degree of bridge adjustment. Byalternately adjusting the bridge and the string tension, the pitch ofthe open string and the pitch of the twelfth fret octave may both betuned. When this is done the other fret positions will .be very closelytuned.

FIG. 2 illustrates one commercial form of the instrument. A small metalenclosure 1 has a power-on and string-frequency-selector switch 4. Theswitch is shown with the pitches of the six strings of a standardelectric guitar: B A D G B and E Other pitches could be incorporated toaccomodate the tuning of other instruments.

Indicator neon lamp 3 provides the visual means of indicating the degreeof tuning.

Jack 2 accepts the signal from electric guitar 6 by way of a cable andphone plug 5 which is inserted.

Audio connector 8 may be inserted in a jack 93 which is mounted on theback of the instrument.

Jack 93 carries a'signal from the selectable standard frequencyoscillator. If, via audio connector 8 and a cable, the signal isconnected to the input of an instrument amplifier-speaker system itwould allow a number of musicians to tune by ear" to the standard pitchselected by switch 4. This does not prevent the guitarist from tuningvisually at the same time and he may thus compare his aural sense oftuning with the more accurate visual indication.

Plug 7 provides a power connection for the instrument to the AC. mains.

In FIG. 4 the jack 2 is shown as providing the input connection for theguitar signal. The guitar signal is coupled thru electrolytic capacitor9 to the base of transistor 14. Collector load resistor 11, base biasresistor l0, emitter resistors 15 and 17, by-pass capacitor 16 togetherwith transistor 14, form a linear amplifier. Base bias resistor 10provides some negative feed-back to the base. This amplifier stage isdesigned to have a quiescent collector voltage of one half the supplyvoltage (+10 volts). Resistor 13 couples the linear amplifier output tothe non-inverting input (pin 5) of operational amplifier l9. Resistor 12together with resistor 20 form a negative feed-back loop from the output(pin 10) to the inverting input (pin 4) of the operational amplifier.This loop establishes the output quiescent point of amplifier 19 atapproximately the same voltage as is present at the collector oftransistor 14.

Resistor 13 is made approximately equal to the parallel combination ofresistors 12 and 20, to minimize drift due to the amplifier inputcurrents.

Under steady state conditions the quiescent voltage at the collector oftransistor 14 is present at both the inverting and non-inverting inputsof amplifier 19. However, when a signal is present at the collector oftransistor 14 it willbe decoupled from the inverting input by capacitor18.

The operational amplifier 19 in this configuration has good quiescentoutput. voltage stability and yet exhibits an open loop gain for thesignal present at its non-inverting input. A low amplitude signal fromthe linear amplifier will cause the output of amplifier 19 to switchbetween the limits of the power supply voltage thereby producing asquare wave of the same frequency as the input.

The quiescent output voltage of amplifier 19 is blocked by capacitor 21.The square wave output signal when present is coupled thru capacitor 21across a resistive divider consisting of resistors 22 and 23. Theresistive divider reduces the amplitude of the square wave and reducesthe loading of the output of amplifier 19. The output of the resistivedivider is, connected to the base of transistor 25 and the cathode ofdiode 24. The square wave signal from the divider will be symetricalwith respect to ground. Since the base of transistor 25 will beconducting for only the positive half cycle, diode 24 must be'used toconduct during the negative half cycle. Otherwise a base rectificationeffect would occur.

With collector load resistor 26 returned to plus 3.6 volts the collectoroutput of transistor 25 will be a square wave limited by ground and plus3.6V.

The square wave output thus limited is connected to one input (pin 1) ofa two-input NAND/NOR gate, one of two such gates contained in integratedcircuit 32. If both inputs tothis gate are low (near zero volts) theoutput will be high (near +3.6 volts). For either or both inputs highthe output will be low.

Circuit point 37 is connected to the output of the selectable standardfrequency oscillator hereinafter to be described. Therefore a sinusoidalsignal of several volts amplitude will-be present at circuit point 37.

The charging and discharging of coupling capacitor 27 is determined bythe subsequent network. For any long term average the charging currentmust equal the magnitude of the discharging current for each cycle ofthe input signal. For a positive-going input signal the charge pathwould be resistor 28 in parallel with the series combination of resistor29 and the emitter-base junction of transistor 30. A negative-goinginput signal would have a discharge path consisting of only resistor 28(the emitter-base junction of transistor 30 would be reverse biased andconsequently non conducting).

Assuming the base-emitter resistance and forward voltage drop oftransistor 30 to be negligible, the transistor could be made to drawbase current for only 60 of the input sinusoidal signal by setting theresistance ratio of resistor 29 to resistor 28 equal to l/27.

With a high current gain, transistor 30 will be saturated for 60 of theinput sinusoidal signal and cut off for the remaining 300.

Resistor 31, the collector load for transistor 30, is connected to theplus 3.6 volt supply. The output signal at the collector of transistor30 will be a series of pulses limited by plus 3.6 volts and ground.

Referring to FIG. 3, waveform A is a square wave signal such as would bepresent at the collector of transistor 25- when the fundamental guitarsignal is above the frequency of the selectable-standardfrequencyoscillator.

Waveform B is the signalpresent at the collector of transistor 30 whenthe proper frequency is being generated by the selectable standardfrequency oscillator.

in H0. 4 pin 1 and 2 of integrated circuit 32 are inputs to a NAND/NORgate the output of which is on pin 7 With the guitar-signal-derivedsquare wave provided as an input to pin 1 and the sample pulses, derivedfrom the selectable standard frequency oscillator, provided as an inputto pin 2, the output signal of the NAND/NOR gate is shown as waveform Cin FIG. 3. The first two sample pulses (B) are in phase with the squarewave (A) and are propagated thru the gate to appear inverted at itsoutput (C). The third sample pulse (B) is propagated thru only until thesquare wave switches. When the square wave switches it disables thegate. Thus only the first part of the third sample pulse. is

propagated thru the gate.

The fourth, fifth and sixth sample pulses (B) occur out of phase withthe square wave (A), which disables the gate, and are thus'notpropagated thru. Theresult from output (C) is a blinking of theindicator lamp at 'an observable frequency equal to the differencebetween the frequencies of (A) and (B).

Waveform D is a square wave signal such aswould be present at thecollector of transistor 25 when the guitar signal is raised by oneoctave. Waveform E is the same as waveform B.

The waveform D is higher in frequency than twice the frequency of theselectable standard frequency.

oscillator.

Sample pulses 1, 3 and 6 (E) are not propagated thru the gate for theirfull duration due to the square wave (D) switching during theirduration. Sample pulse 2 (E) is out of phase with the square wave (D)and thus is not'propagated to the output of the gate (F). Sample pulses4 and 5 (E) occur in phase with the square wave (D) and are fullypropagated thru the gate. They appear inverted at the output (.F). Theresult from output (F) is again a blinking of the indicator lamp but ata higher rate than for output (C).

When the guitar signal fundamental frequency matches the frequency ofthe selectable standard frequency oscillator, the output of the gatewill either be a continuous stream of pulses or no pulses at all. Sincethe two frequencies match, there will be no relative shift of phase andthe gate output will be determined by the random phase relationshipestablished when the instrument string is plucked.

If the guitar signal is exactly an octave higher than the frequency ofthe selectable standard frequency oscillator the sample pulses willoccur every other cycle of the square wave and the relative phase willnot change. The output of the gate will again be determined by therandom phase relationship established when the instrument string isplucked.

As can now be seen, the sample pulse is made less than 25 percent of theperiod of the fundamental frequency in order to check the tuning of thestring ata frequency one octave higher than the fundamental. In theorythe sample pulses may be made shorter to check higher octaves but otherconsiderations make more than two octaves impractical. if thefundamental were the only frequency to be tuned the sample pulses could.be almost as wide as one half the period of the fundamental.

The output of the gate of FIG. 4, the operation of which was justdescribed, (pin 7) is connected to an input (pin 3) of a second NAND/NORgate in integrated circuit 32. The second input (pin 5) of the gate isgrounded, therefore the gate secures only to invert the signal from thefirst gate. The output of the second gate (pin 6) willbe the complementof the output of the first gate (pin 7).

As was shown in FIG. 3 (waveforms C and F) the output of the first gate(pin 7) is low (near zero volts) in the absence of propagated samplepulses. The propagated sample pulses cause the output (pin 7) to go high(near +3.6 volts).

Since the second gate complements its input, the output (pin 6) will behigh" in the absence-of propagated sample pulses and will go low witheach propagated sample pulse. 7 v

The output of the second gate ,(pin 6), thru current limiting resistor33, controls the base current of a high voltage switching transistor 35.When theoutput of the second gate (pin 6) is high, (near +3.6 volts)sufficient base current is provided to transistor 35 to saturate it. Thecollector voltage of transistor 35 will be near zero. All collectorcurrent thru collector load resistor 36 from the 100V supply will flowthru transistor 35 to ground and the glow-discharge indicator lamp 3 isextinguished.

A low output (near zero volts) from the second gate (pin 6) will befurther reduced by the division of voltage by resistors 33 and 34,ensuring that the voltage at the base of transistor 35 will be belowthat required for base current flow.

Transistor 35 is thus in a non-conducting state and the collectorvoltage will rise, limited only by the ignition voltage of theglow-discharge indicator lamp 3 which is now lit.

Thus, when a sample pulse is propagated thru the first gate (pin 7) itwill cause glow-discharge indicator selected between switch decks 4,,-and 4, and resistor 57 in series with the trimmer potentiometer selectedby switch deck 4,. The second section consists of the capacitanceselected between switch decks 4,, and 4 and resistor 76. The thirdsection consists, of the capacitance selected between switch decks 4 and4,, and the parallel combination of the resistance of resistors 77 and79.

Switch 4 consists of 6 decks 4A, (shown in FIG. 6)4B,4C,4D,4E and 4F.All decks are shown in the full counter clockwise, or power off,position. Turning the switch one or more positions clockwise will turnpower on as is shown in FIG. 6.

in the first clockwise position capacitors 75, 72, 69, 66, 63 and 60 areparalleled in the first section of the network, and the resistance istrimmed by potentiometer 51 for the proper frequency. In the secondsection of the network capacitors 74, 71, 68, 65, 62 'and 59 areparalleled. in the third section of the network, capacitors 73, 70, 67,64, 61 and 58 are paralleled. This position of switch 4 corresponds tothe lowest frequency, E (82.4 H,), of the oscillator. V

In the second clockwise position capacitors 75, 74 and 73 have beendisconnected from the first, second and third network sectionsrespectively. The total parallel capacitance of the sections is reducedand the frequency generated is higher, A (110.014,). Poten tiometer 52provides means to adjust this frequency accurately.

in each successive clockwise position, the

, capacitance of each section of the network is reduced by thedisconnecting of capacitors 70, 71 and 72 (third position), 67, 68 and69 (fourth position), 64, 65 and 66 (fifth position) and 61, 62 and 63(sixth position). in the sixth position, only capacitors 60, 59 and 58are operative in the circuit. I

The frequencies may be adjusted by potentiometers 53, 54, 55 and 56which corresponds to D; (146.8H,), G (l96.0H,), B (246.9H,) and E,(329.611,) respectively.

Resistors 77 and 79 (the parallel combination of which form theresistance of the last network section) form a voltage divider whichbiases the gate of an N- channel field effect transistor 78. Source loadresistor 80 completes the source-follower circuit configuration. Thesource-follower circuit provides a high impedance input for minimumloading of the phase-shift network and'a low impedance non-invertingoutput with less than unity gain. Capacitor 81 couples the signal fromThe amplitude of the oscillation, normally limited by.

the supply voltage, is further limited by the loading of the resistivedivider, consisting of resistors 86 and 87, thru diode 88. Quiescently,the collector voltage of transistor 84 is lower than the voltage at thecathode of diode 88. Thus, until the signal at the collector exceeds thevoltage at the cathode of diode 88, the resistive divider does not loadthe collector of transistor 84. For

the period of time when the signal does exceed the voltage at thecathode of diode 88, the effective collector load resistance oftransistor 84 will consist of the parallel resistance of resistors 83,86 and 87. This parallel resistance is below the resistance required asa collector load to sustain oscillations. The signal is thus limitedwith negligible distortion.

Transistor 89 together with emitter load resistors 90 and 91 form anemitter-follower circuit. The collector output of transistor 84 isdirectly coupled to the base of transistor 89. The emitter-followerprovides a high inputimpedance, negligible loading of transistor 84, anda low output impedance sufficient to drive the phase shift network.Circuit point 37, the output of the emitter-follower, is connected tothe input of the pulse forming circuit shown in FIG. 4. A small fractionof the emitter-follower output signal is coupled to jack 93 by capacitor92. Jack 93 is located on the rear of the metal enclosure 1 shown inFIG. 2. The usual instrument amplifier-speaker unit, with the signalfrom jack 93 as its input, may be used to provide selectable pitches foraural tuning. Several members of a band could thus tune aurally at thesame time the guitarist is tuning visually.

In FIG. 6 circuit points7A and 7B are connected to the plug 7 shown inFIG. 2. A.C. power is thus supplied to transformer primary 37A oftransformer 37 thru power switch 4A, operated with selector switch 4 ofFIG. 2.

The output voltage of secondary winding 37 B is halfwave rectified bydiode 38 and filtered by capacitor 39. The unregulated 100 V.D.C. supplythus formed is used to power the glow-discharge indicator lamp circuit.

Diodes 40 and 41 full-wave rectify the output voltage of secondarywinding 37C. The rectified output voltage, filtered by capacitor 42,supplies two voltage regulators.

Current limiting resistor 44 together with zener diode 43 form a simpleshunt voltage regulator. The regulated voltage (+3.6V) suppliesintegrated circuit 32 and the collector circuits of transistors and ofFIG. 4.

Transistor 46 of FIG. 6 is the series regulator for the second regulatedsupply.

The base voltage of transistor 46, and consequently the output voltage,is controlled by the voltage reference and error amplifier 47. Basesupply resistor 45 forms the load resistance for voltage reference anderror amplifier 47. The output voltage is determined by the ratio of theresistance of resistors 48 and 49 and the internalvoltage reference inamplifier 47. Capacitor 50 serves to filter any higher frequency signalsthat would be generated by the driven circuits to which the regulatormay not respond. This regulated supply voltage (+20V) powers theselectable standard frequency oscillator (FIG. 5) and the saturatingamplifier (collector circuit of transistor 14 and integrated circuit 19)of FIG. 4.

While the foregoing are examples of specific circuitry and components,it will be understood by those skilled in the art that the invention isnot limited thereto and may be practiced with other circuitry for thetuning of any stringed musical instrument.

I claim:

1. An electronic tuning device for stringed instruments comprising: I

a. a high-gain saturating amplifier having an input for the picked-upsignal of the string to be tuned; said amplifier including circuit meansfor converting the decaying sinusoidal signal of the string into asquare wave output signal of the same frequency and lasting from 5 to 10seconds; a generator of a reference frequency; circuit means connectedto said generator for converting the reference frequency into outputpulses of the same frequency; an electronic gate having a first inputconnected to receive said square wave output si nal and a second inputconnected to receive sai output pulses;

f. circuit means connected to said gate and operative to deliver anoutput from said gate only when the first and second inputs aresimultaneously present and of the same phase;

. a glow lamp connected to receive the output from said gate to therebyindicate visually the frequency difference between the square wave andthe pulses;

said circuit means converting the reference frequency into output pulsesbeing constructed to produce a pulse width less than 25 percent of saidsquare wave wavelength, whereby the lamp responds to tune a next higheroctave.

2. The device of claim 1 having a plurality of generatory of referencefrequencies and switching means to selectively render operable each ofsaid generators.

3. The device of claim 2 wherein each of said generators is formed by aresistor-capacitor network and each generator includes a trimmerresistor to standardize the frequency thereof.

4. The device of claim I having connecting means leading from saidgenerator to deliver a reference frequency to an amplifier-speaker foraural tuning of a band.

1. An electronic tuning device for stringed instruments comprising: a. ahigh-gain saturating amplifier having an input for the picked-up signalof the string to be tuned; b. said amplifier including circuit means forconverting the decaying sinusoidal signal of the string into a squarewave output signal of the same frequency and lasting from 5 to 10seconds; c. a generator of a reference frequency; d. circuit meansconnected to said generator for converting the reference frequency intooutput pulses of the same frequency; e. an electronic gate having afirst input connected to receive said square wave output signal and asecond input connected to receive said output pulses; f. circuit meansconnected to said gate and operative to deliver an output from said gateonly when the first and second inputs are simultaneously present and ofthe same phase; g. a glow lamp connected to receive the output from saidgate to thereby indicate visually the frequency difference between thesquare wave and the pulses; h. said circuit means converting thereference frequency into output pulses being constructed to produce apulse width less than 25 percent of said square wave wavelength, wherebythe lamp responds to tune a next higher octave.
 2. The device of cLaim 1having a plurality of generator of reference frequencies and switchingmeans to selectively render operable each of said generators.
 2. Thedevice of cLaim 1 having a plurality of generator of referencefrequencies and switching means to selectively render operable each ofsaid generators.
 3. The device of claim 2 wherein each of saidgenerators is formed by a resistor-capacitor network and each generatorincludes a trimmer resistor to standardize the frequency thereof.
 3. Thedevice of claim 2 wherein each of said generators is formed by aresistor-capacitor network and each generator includes a trimmerresistor to standardize the frequency thereof.
 4. The device of claim 1having connecting means leading from said generator to deliver areference frequency to an amplifierspeaker for aural tuning of a band.4. The device of claim 1 having connecting means leading from saidgenerator to deliver a reference frequency to an amplifier-speaker foraural tuning of a band.